Polymer blends of ethylene-propylene (EP) polymers or of ethylene-propylene-diene (EPDM) polymers with .alpha.-monoolefin polymers, particularly with polyethylenes, are known in the art (see U.S. Pat. Nos. 3,176,052; 3,328,486; 3,361,850 and 3,751,521). At times, curing or crosslinking agents are added to effect chemical changes in the nature of the blend (see U.S. Pat. Nos. 3,564,080 and 3,806,558). Polymer blends described in U.S. Pat. Nos. 3,785,643 and 3,806,558 are stated to be thermoplastic in nature. They are prepared by partially crosslinking the polymers, particularly the EPDM polymers.
U.S. Pat. No. 3,835,201 is directed to blends of EPDM or EP polymers having high zero shear viscosity, together with a polyolefin resin (such as polyethylene, polypropylene or a crystalline EP copolymer). U.S. Pat. No. 3,741,924 teaches blends of an EPDM polymer, an ethylene-.alpha.-olefin copolymer and a tackifier. U.S. Pat. No. 3,906,056 discloses blends of an EPDM rubber and an amorphous EP block copolymer. Finally, U.S. Pat. No. 3,919,358 teaches blends having superior tensile strength comprising an EPDM polymer having a high degree of unstretched crystallinity, together with a polyethylene.
The polymer blends of the present invention are thermoplastic in nature, and do not require curing or crosslinking agents in their preparation. Additionally, the tensile strengths of the blends of the present invention are superior to that predicted from the individual contributive effects of the polymer components, i.e., greater than any one polymer component of the blends. Such blend properties are attainable using EPDM and EP polymer components having specific ranges of ethylene content, unstretched crystallinity, and Mooney viscosity. Blend tensile strengths may be improved further by including therein at least one polyethylene.